Methods for biometric identification based on facial features, including features of the eye are known. Methods for iris recognition implement pattern-recognition techniques to compare an acquired image of a subject's iris against a previously acquired image of the subject's iris, and thereby determine or verify identity of the subject. A digital template corresponding to an acquired iris image is encoded based on the image, using mathematical/statistical algorithms. The digital template is compared against databases of previously encoded digital templates (corresponding to previously acquired iris images), for locating a match and thereby determining or verifying identity of the subject.
Apparatuses for iris recognition may comprise an imaging apparatus for capturing an image of the subject's iris(es) and an image processing apparatus for comparing the captured image against previously stored iris image information. The imaging apparatus and image processing apparatus may comprise separate devices, or may be combined within a single device.
While iris recognition apparatuses have been previously available as dedicated or stand alone devices, it is increasingly desirable to incorporate iris recognition capabilities into mobile communication devices or mobile computing devices (collectively referred to as “mobile devices”) having inbuilt cameras, such as for example, mobile phones, smart phones, personal digital assistants, tablets or laptop devices.
It has however been found that cameras within mobile devices are intended to operate as general purpose cameras, capable of capturing images of objects situated at a wide range of distances from the mobile device. The considerations for acquiring iris images for the purpose of biometric recognition are significantly different from considerations applicable to image capture of non-iris images. Specifically, iris imaging particularly necessitates positioning of a subject's iris within a defined image capture region, such that the iris image acquired by the imaging apparatus satisfies a minimum pixel resolution in the object plane. Given the size of the iris, and pixel size of image sensors typically used in mobile device cameras, configuring a camera to capture an iris image having suitable iris diameter in the image plane, requires a specific object distance (i.e. distance at which the subject's iris requires to be positioned). Configuring a camera inbuilt into a mobile device in this manner may render the camera unsuitable for multiple uses (such as for iris imaging while retaining general purpose photography capabilities) by requiring that the object be placed very close to the camera to obtain images having appropriate sharpness and detail.
Prior art solutions for altering an object plane of a camera typically involve a zoom lens type arrangement, where the lens assembly comprises a number of individual lenses that may slide axially along the body of the lens assembly to change focal length and magnification of the lens assembly. However, zoom lenses are expensive and bulky, both of which provide serious disincentives for use in cameras inbuilt into mobile devices.
Another concern that arises from dual use of fixed focus cameras, is that iris image capture typically relies on infrared (IR) wavelengths, whereas non-iris image capture usually seeks to eliminate IR wavelengths by using IR cut filters (filters which reflect or absorb IR wavelengths, while allowing visible wavelengths to pass through the lens assembly and on to the image sensor).
It is therefore an objective of the invention to provide efficient and cost effective mechanisms to configure an iris imaging apparatus or camera built into a mobile device such that the iris imaging apparatus or camera can be optimized for iris imaging.